In the development of fire doors, it is recognized that the door should be arranged for closure by means independent of power sources which may be damaged by the same fire which the door is intended to guard against. Accordingly, fire doors are normally made for closure in response to gravity and a variety of arrangements for this purpose are well known. For this purpose, roll-type doors comprising horizontal metallic slats are in many instances highly advantageous due to their minimal space requirements for installation and due to their being out of the way above the door when in an inactive condition.
There has, however, been a continuing problem with such doors in that when they are sufficiently counterbalanced by internal torsion springs to render them reasonably easy to open, they tend to have insufficient closing tendency in response to gravity to be reliable. On the other hand, when the counterbalancing is weakened sufficiently to insure prompt and positive closing, the door then becomes relatively difficult to open or when closing it may do so too rapidly and inflict injuries upon persons who may be in a position thereunder. Thus, it is not only extremely difficult to adjust the torsion of the counterbalancing springs sufficiently accurately to obtain the desired action, but same may change after adjustment due to fatiguing of the metal or due to the ambient heat generated by the fire against which the door is intended to close.
In attempting to meet this and other problems of fire door constructions of this general type, it has in the past been known to initiate rotation of the door-carrying roll by some type of spring-loaded or weight-responsive device upon the occurrence of an appropriate signal, such as the melting of a fusible link, and permitting the door thereupon to continue its descent by gravity. Inasmuch as the gravitational force progressively increases as the door unwraps, this still results in severe shock to the door which could even be sufficiently severe to cause serious damage thereto. In an attempt to meet this problem, the prior art has provided speed limiting devices generally similar to a clock escapement wherein the door applies power thereto in the manner of clock weights and the escapement limits the speed at which the door can descend. This, however, has presented difficulties in the past due to insufficient power applied by the door to the escapement mechanism when the door is only starting to unwrap. This can be especially true if the mechanism has stood stationary for several months, or even years, with such accumulation of dirt and other contaminants as to render its moving parts stiff and requiring considerable force to overcome the friction present therein.
It has therefore long been desirable to devise a door construction which will effect a positive and certain starting of the unwrapping movement of the door, which will reliably limit the ultimate speed of descent of the door, but which will provide a minimum of frictional or other obstruction to the descent of the door in its initial descending condition, and which when the door moves slowly will not add to or increase the frictional resistance applied thereto.
Accordingly, the objects of the invention include:
1. To provide a roll-type fire door having horizontal metal slats, together with an operator, hand operated chain hoist, hand crank or other mechanical means of opening and closing the door during normal conditions, whereby the door will normally be held in an open position, will respond to ambient heat above a predetermined level to permit same to close by gravity and wherein such closure will be positive and certain but yet sufficiently controlled to insure against injury to the door or to persons thereunder.
2. To provide a fire door together with door operating means, as aforesaid, including means immediately responsive to said ambient temperature for positively initiating downward movement of such door. 3. To provide a fire door together with door operating means, as aforesaid, including centrifugal brake means by which the speed at which said door closes may be selected and controlled as desired.
4. To provide a fire door together with door operating means, as aforesaid, including mechanical assist, or power driven, means for opening said door, which means will be automatically disconnected simultaneously with initiation of door closure movement whereby such means will not interfere with the gravity induced closure movement of the door.
5. To provide a fire door and operator means, as aforesaid, including mechanical assist or power driven means for opening said door, which last-named means may be manually or pedally re-engaged after closure of the door for reopening same, as for emergency escape use, but which will then automatically permit the door to reclose when the manual or pedal operation is removed.
6. To provide a fire door and operator means therefor, as aforesaid, which will throughout be of relatively simple but sturdy construction, which will be free from the necessity for fine or delicate adjustments, which can stand inoperative for long periods of time without material change in operating characteristics and which will in all respects be reliable for operation in its intended manner.
7. To provide a fire door and operator means therefor, as aforesaid, which will utilize in large measure presently known roll-type door construction, (and thus require relatively little additional special equipment), whereby to obtain the objectives above set forth at a minimum of cost.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspection of the accompanying drawings.